Methods of cutting a work made of a polymer material are mainly with a blade or a metal mold. In the cutting of a polymer material using a blade or the metal mold, foreign substances from the cut may be generated from the work due to the impact of cutting, and the foreign substances may fall off from the cut surface. Therefore, there has been a necessity to improve the processing accuracy of the cut surface and to improve the quality of the product.
Cutting by a laser beam has been investigated, for example, as a method of cutting to improve the quality of the processed product. Cutting by a laser beam makes it possible to reduce the cut foreign substances generated when the blade, etc. is used. However, with this method, a polymer material that is radiated with the laser beam changes into a gas due to thermal decomposition, and a phenomenon that is similar to an explosion occurs. Also, there is a problem that the generated gas contaminates the surface of the work.
For example, when a laser beam 12 is irradiated from the vertical direction to a work 11 as shown in FIG. 2, a gas 13 that is generated due to the decomposition of the polymer material diffuses in the direction parallel to the surface of the work 11. Therefore, the surface of the work 11 is contaminated by the gas 13.
As disclosed in Patent Document 1, a method has been considered of cutting a work made of metal by irradiating a laser beam from a direction that is tilted by a prescribed angle opposite to the advancing direction of cutting. This method has an effect of improvement for melted substances that attach to the backside of the work. However, the gas that is generated due to the decomposition of the metal advances and diffuses in the direction parallel to the surface of the work as shown in FIG. 3. Therefore, the surface of the work is contaminated even with the method described in Patent Document 1.
A method of cutting is disclosed in Patent Document 2 in which an improvement for melted substances on the backside is investigated by using a work made of a plastic material. However the contamination of the surface of the work cannot be prevented even with this method.    Patent Document 1 Japanese Patent Application Laid-Open No. 02-290685    Patent Document 2 Japanese Patent Application Laid-Open No. 2001-262083